I feel Waluigi would be saved for the base roster of the next Smash game like K Rool & Ridley were. He’d be the easiest way to get attention for that game especially if they do have to cut a lot of characters.
If we get another Mario character in Ultimate then it’s absolutely Geno.
Besides, their would be FAR more content in a Geno Challenger Pack then a Waluigi pack. SMRPG has zero representation in Smash besides a measly two Spirits, and they could totally bring new content from that game. Their is just so much potential for stages, music and Spirits as most of the locations, music and characters are original and unique to Mario.
As a Waluigi supporter, even I struggle with what Waluigi could bring for a Challenger Pack. I guess Waluigi Pinball makes sense as his stage, but would they really make a Waluigi-themed stage as the second brand new Mario stage in Ultimate? Besides, Waluigi Pinball already has a remix in Smash so I see no reason why Sakurai would want that as a stage. As for music, they could bring music from Mario Sports games, but I don't see how any of the music they could bring to Smash would relate at all to
Waluigi. As for Spirits, they could have the OC's from the Mario Tennis and Golf games, but what could they do for these Spirit battles to make them different? And again, how would they relate to Waluigi?
That is why I feel Geno is far more appropriate for a Challenger Pack. Their is so much potential to be had with an SMRPG-themed pack that its honestly absurd. As for Waluigi, while their are some ideas, I feel like none of them would relate to his character at all and would just be filled with randomness, and I don't think Sakurai really wants to do that with these Packs